Patients receiving combination therapy for chronic hepatitis C virus (HCV) infection (standard or pegylated interferon alfa [PEG-IFN] in combination with ribavirin [RBV]) frequently develop moderate to severe anemia. In large, prospective, clinical trials of PEG-IFN alfa-2b and PEG-IFN alfa-2a, the reported mean decreases in hemoglobin (Hb) were 2.5 g/dL, and 3.7 g/dL, respectively. Furthermore, in a retrospective study, 54% of standard interferon/RBV-treated patients had hemoglobin decreases of at least 3 g/dL. It is important to understand the causes, natural history, and risk factors associated with HCV therapy-induced anemia, because such decreases in hemoglobin can result in RBV dose reduction or discontinuation, which may decrease the likelihood of a virologic response by patient. Erythropoietin is an endogenous hormone that acts in the bone marrow to increase the number of erythroid progenitor cells (red blood cells). Normally, a decrease in the hemoglobin level is accompanied by an increase in the serum erythropoietin (sEPO) level, which will ultimately normalize the Hemoglobin level. The relationship between hemoglobin and serum erythropoietin is less apparent in patients with chronic diseases such as cancer and human immunodeficiency virus (HIV) infection. It is not known whether HCV/HIV co-infected patients receiving combination PEG-IFN/RBV therapy have a similarly diminished erythropoietic response to anemia. The objective of this study is to document the pattern of hemoglobin changes and erythropoietic response (from baseline to final assessment) in HCV/HIV co-infected patients receiving combination therapy with IFN / RBV. N/A